WASHINGTON — Senate Republican leaders are altering their tax bill to include a repeal of the Affordable Care Act’s individual mandate, a major change as they now try to accomplish two of their top domestic priorities in a single piece of legislation.

Party leaders said Tuesday their tax bill will include a provision that would repeal the individual mandate, a part of the health care law that creates penalties for Americans who don’t have insurance.

‘‘We’re optimistic that inserting the individual mandate repeal would be helpful,’’ Senate majority leader Mitch McConnell of Kentucky, said Tuesday after meeting with fellow Republicans.

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Party members had resisted making the change, worried that injecting health care politics would imperil the tax bill. But many
have supported adding the repeal, a move President Trump has pushed repeatedly as well.

Repealing the mandate would free up more than $300 billion in government funding over the next decade, but it would also eventually lead to 13 million fewer people having health insurance, according to projections from the Congressional Budget Office.

Senator John Thune, chairman of the Senate Republican Conference and a member of the Finance Committee drafting the tax bill, said repealing the individual mandate will allow them to further cut taxes for some families.

‘‘It will give us even more of an opportunity to really distribute the relief to those middle-income cohorts who could really benefit from it,’’ the South Dakota senator said.

But the change could unnerve less conservative Republican senators, who voted against previous Senate efforts to repeal large parts of the Affordable Care Act.

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Republicans appeared to give differing explanations for what they would do with the extra money generated by repealing the individual mandate.

McConnell, speaking later at an event hosted by The Wall Street Journal, said the repeal would allow them to ensure corporate tax cuts remain permanent while lowering taxes for middle-class families.

‘‘It’s pretty appealing to us, and it will be in the version that comes out of the Finance Committee this week,’’ McConnell said.

Trump has said the repeal should be focused on getting tax rates down for companies, with any leftover going toward cutting taxes for the middle class.

In addition to repealing the individual mandate, the updated tax bill could also include a bipartisan health care agreement recently reached by Senators Lamar Alexander, Republican of Tennessee, and Patty Murray, Democrat of Washington, according to Republican Senators Bob Corker of Tennessee and Susan Collins of Maine.

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That Murray-Alexander agreement would fund federal subsidies used to help lower-income Americans afford their health care.

The tax bills in the House and Senate would lower taxes for many Americans, but nonpartisan analysts have concluded millions would pay higher taxes, particularly if they lived in states such as New York, Massachusetts, and California.

House GOP leaders have said they would explore whether to include a repeal of the individual mandate in their version of the tax cut bill, but they have so far not made that change.

They are hoping to vote on their version of the measure as soon as Thursday.